This invention relates generally to material handling vehicles and, more particularly, to an improved system for monitoring lift chains within such vehicles.
The high cost of warehouse space makes it economically desirable to provide high racks for storing materials within a warehouse. Due to the vertical extension of storage in warehouses, a variety of material handling vehicles have been developed wherein material handling devices, typically forks, are elevated to extreme heights to store and retrieve materials at the upper levels within the warehouse.
Such high lift vehicles commonly use a variety of mast arrangements wherein the forks and oftentimes even the operator of the vehicle are lifted high above the floor of the warehouse to perform these storage operations. While the masts and forks are normally controlled by means of hydraulic systems which can exert the necessary forces required to move the heavy machines and materials, it is the case in many designs that the masts have chains for transmitting the hydraulic power to the masts and/or forks for vertical movement. Typically, one or often two chains are provided which chains are normally taut during operation of the material handling vehicle.
In two chain or duplicated chain systems, it is known to monitor the chains so that if one of the chains breaks, the material handling vehicle can be stopped and repaired prior to further operation. However, a broken chain is sensed by the detection of slackness in the chain. Hence, if the forks or a portion of an elevated platform hangup or catch on a rack or other obstruction as they are being lowered, slackness may develop in the chains and this slackness may be sensed as a broken chain resulting in the vehicle being disabled until it can be serviced. Such unwarranted interruption of the operation of a material handling vehicle can be costly.
Thus, it is apparent that the need exists for an improved chain monitoring system for use on material handling vehicles which are utilized to handle heavy materials oftentimes at high elevations in warehouse storage racks.